Resistance to the effects of object impact, radiation, thermal distortion and thermal stresses are desirable in composite material laminates used in different types of structures where dimensional precision, high strength and light weight are preferred.
It is desirable to have high strength lightweight composite structures that can be used on aircraft, spacecraft, satellites, missiles, and the like that are resistant to impact damage from various types of objects. For instance, aircraft and spacecraft need protection from impact with foreign objects, such as rain, birds, rocks, dirt, micro-meteoroids, and orbital debris. For some types of aircraft, foreign objects will typically approach at velocities less than that of sonic velocity, approximately 0.3 km/second and cause damage to the aircraft. For spacecraft, foreign objects may approach at a high velocity or hyper velocity, in the range of 10 to 72 km/second and cause damage to an unprotected spacecraft.
In some instances, mechanical shields have been used to protect aircraft and spacecraft, such as aluminum shields. A typical aluminum shield consists of an outer aluminum wall and an inner aluminum wall enclosing a multi-layer material located in between. The multi-layer material may be selected for thermal insulating and/or shock dispersion properties, fabricated using metal foils or ceramic fabrics. However, mechanical shields impose a weight and instrument line of sight penalty on the craft to which they are applied.
High altitude aircraft, missiles, and space related craft benefit from radiation shielding using materials such as boron, tungsten, titanium, tantalum, gadolinium, hafnium, osmium, platinum, gold, silver, or palladium, or combinations thereof. Early radiation shielding materials for semiconductor devices have been made of a gold plated tungsten-copper alloy. Foils formed of such materials used in composite structures incorporated into the walls of spacecraft, and the like, are costly to fabricate, and are prone to warpage or mechanical failure in use because the organic adhesive used between the metal foil and other materials of the composite structure each have different coefficients of thermal expansion. Additionally, the adhesive bonds between dissimilar materials are not as robust as bonds between like materials and require proper processing.
Aircraft, missiles, and space related craft using composite structures also require protection from lightning strikes and Electro-static Discharge (ESD) from surface charging. Structures were initially protected from lightning strikes using rods and cables to ground the structure. Recently, aircraft and other metal structures were provided lightning protection by using a low resistance pathway through the structure as a means for energy dissipation from the lightning strike. However, composite structures formed of composite materials using thermosetting and thermoplastic polymer impregnated fiber reinforcement do not have sufficient surface conductivity with low resistant pathways for energy dissipation from lightning strikes or ESD. Carbon/graphite fiber within the matrix offer higher conductivity than fiberglass materials or high temperature thermoplastic reinforced materials but are still deficient for energy dissipation from lightning strikes or ESD. In some instances, multi-layered composites include metallic wire screen or foil layers in an attempt to deal with lightning strikes and ESD, and also Electromagnetic Interference (EMI) and Electromagnetic Pulse (EMP). Spacecraft ESD/EMI/EMP prevention requires grounding of the surface and other conductive elements to bleed charge between dielectric regions.
Composite structures on aircraft and spacecraft are subject to thermal stresses from both high temperatures and low temperatures. Composite structures on aerospace vehicles are subject to aero-convective heating and radiant heating as well as being subject to launch acoustics, rain, and other elements of the environment. Spacecraft are subject to heating from solar radiation and shadow cooling. The composite structure may use a multi-layer construction using various layers of metal foil, ceramic spacers, fibrous spacers, plastic layers, silica cloth, glass cloth, fibrous silica felt, and various combinations of such materials. Many aerospace structures for reflectors and instruments preferably comprise low CTE and low thermal distortion.